The present invention refers to a device for applying an elastomeric filler on the bead core of a pneumatic tire.
As known, pneumatic tires for motor vehicles in general are always provided, at the bead, with annular elements of metallic material, usually called bead cores, which have mainly the function of supporting the whole pneumatic tire structure.
In fact, each bead core is anchored to the carcass of the pneumatic tire through a turn-up formed by the plies provided in the sidewalls of the tire, folded as a book around the section of the bead core.
In order to prevent the formation of air pockets between the ply skirts turned-up around the bead core, a suitably shaped filler of elastomeric material is provided along the circumferential chafer of the bead core. The filler has also the task of stiffening the structure of the bead.
Known, apparatuses apply the filler on the bead core in a completely automatic manner.
To this end, these apparatuses use devices in which the filler, previously cut as a strip of suitable length, is tangentially inserted between two coaxially facing pressure discs that, rotating, apply the strip along the circumferential outer chafer of the bead core while this latter, mounted on a suitable bearing element, is rotated around its own axis. Subsequently, a splicing device operates in such a way as to join the opposite ends of the filler that mutually face each other according to a "V" configuration in consequence of the difference of diameters according to which the lower and upper zones of the section of the filler are bent.
In the devices used at present for applying the filler, the bead core is pulled into rotation by one of the pressure discs. In fact, the pressure discs are rotated by a motor, and one of them has a peripheral portion acting against the bearing element of the bead core to pull it into rotation together with the bead core mounted thereon.
Moreover, it is provided that the pressure discs engage the filler through respective perimetric projections obtained on the front of the same so as to be placed into contact on opposite sides of the filler itself, in proximity of the base portion of this latter. The perimetric projections are spaced in a measure slightly smaller than the width of the filler section in the zone where the projections must make contact. Therefore, when the filler is obliged to pass between the pressure discs 14 suffers such a compression on the sides as to produce a force of reaction that thrusts the filler itself against the outer peripheral surface of the bead core, on which a suitable solution has been previously distributed for providing the adhesion of the filler.
From the foregoing it is noted that the known devices for applying the filler reveal some drawbacks.
A first drawback consists in the fact that the filler tends to be lifted from the bead core when it is being released from the pressure discs. In fact, owing to the mutual arrangement of the above said perimetric projections, the filler is compressed on the sides when it is inserted between the pressure discs and, therefore, it exerts on the perimetric projections an elastic reaction that makes it adhere to the projections themselves.
Consequently, the filler is inclined to be removed from the bead core at the points in which the perimetric projections move away from the bead core in consequence of the rotation of the pressure discs. All this can produce several complications in the case in which, for instance, owing to a not so perfect distribution of the solution on the bead core or, in the case in which the solution is not qualitatively satisfactory, the filler should remain attached to the pressure discs instead of adhering to the bead core. In any case, the described solution is not at all favorable for a correct application of the filler on the bead core.
Another drawback is given by the fact that the pressure discs, in order to pull into rotation the bead core, must necessarily be maintained immovable with respect to the bearing element. This determines an irregular application of the filler when, as often happens, the latter has slight dimensional variations of its section. In particular, when the filler has a section of a measure slightly greater than the nominal one, it is subject to suffer an excessive compression when inserted between the pressure discs. This compression may cause an undesirable elongation of the filler along the zones adjacent to its base.
If, on the other hand, the filler has a section of a measure slightly smaller than the nominal one, it may happen that the filler is not sufficiently compressed on the bead core during its application. This may cause a not so perfect adhesion of the filler on the bead core.
Another drawback derives from the fact that the pulling of the bearing element by the corresponding pressure disc takes place according to contact profiles that, nearly always, have radii different from the radius of the outer circumferential chafer of the bead core and from the radius of the perimetric projections positioned to pull the filler. The result is that often the pressure discs pull the filler at a speed different from the speed of the outer perimetric chafer of the bead core, on which the filler leans. This situation, besides not being favorable for a good adhesion of the filler to the bead core, may cause undesirable structural deformations of the filler in its sense of longitudinal development.